Japanese Patent Laying-Open No. 2002-225578 has disclosed a hybrid driving apparatus in which at least a part of paths transmitting powers from a plurality of power sources to wheels are formed of a common path, and a power state control device that changes a state of power transmission between two rotation members is arranged in a path transmitting a power provided from a predetermined power source among the plurality of power sources to the wheels.
According to this hybrid driving apparatus, even when the state of the power transmission between the two rotation members is to be changed for transmitting the power from the predetermined power source to the wheels, the power of the power source other than the predetermined power source is transmitted to the wheels, which avoids lowering of the torque transmitted to the wheels.
When a transmission mechanism that can selectively set a plurality of gear ratios is employed as the above power state control device, the torque provided from the predetermined power source can be increased or decreased for transmitting it to the wheels. FIG. 6 in Japanese Patent Laying-Open No. 2002-225578 has disclosed a structure in which a gear ratio can be switched between two gears, i.e., a low gear (LOW) and a high gear (HIGH) according to a vehicle speed.
In the hybrid driving apparatus described above, when a shift operation is to be performed from the high gear to the low gear, an engaging operation is performed in such a state that the rotational speed of the power source connected to the transmission mechanism in interest has been substantially raised to a rotational speed corresponding to the low gear, and thus, a so-called “clutch-to-clutch” is executed,
Therefore, in the shift operation from the high gear to the low gear, i.e., when the currently selected gear ratio is to be raised to the larger gear ratio, it is necessary to increase the output from the power source and thereby to raise the rotational speed. This output control of the power source is executed by the shift control system governing the shift operation.
When a drive operation, e.g., on an accelerator pedal is performed to request a larger vehicle drive power, it is necessary to increase the output of the power source in interest. Usually, the output control of the power source according to this drive operation is executed by a run control system that governs vehicle running and is arranged independent of the shift control system.
As described above, the two control systems can operate independently of each other in the operation of shifting from the high gear to the low gear, and therefore it has been required to find out an optimum switching manner for these control systems. More specifically, when the run control system is selected on a priority basis, such a problem occurs that the rotational speed of the power source cannot be raised rapidly, and the shift operation delays. Conversely, when the shift control system is selected on a priority basis, this causes a problem of lowering a response of a vehicle behavior to a drive operation. Further, such a problem occurs that the output torque of the power source may change rapidly to apply a shock to a driver and/or passenger(s) depending on the timing of switching between the shift control system and the run control system.